1. Field of the Invention
The present invention generally relates to a sample handling unit applicable to a microchip, and a microfluidic device having a plurality of microchips. More specifically, the invention relations to a sample handling unit capable of being widely applied to a microchip (e.g., a microchip of a type for moving a very small amount of sample (specimen) in a microchannel, or a microchip of a type for housing and holding a very small amount of sample (specimen) in a microwell) or the like in a technical field called integrated chemistry, and the invention also relates to a microfluidic device which is used for carrying out the separation, analysis or the like of a very small amount of sample in a fluid, or for carrying out the mixing, reaction, concentration or the like of a very small amount of sample.
2. Description of the Prior Art
In recent years, there is known a technique called integrated chemistry for forming a fine groove (recessed portion) having a width and depth of about tens to two hundreds micrometers in a microchip (sample handling unit) of a glass or plastic, to use the fine groove as a liquid passage, reaction vessel or separation/purification detecting vessel, to integrate a complicated chemical system into the microchip. According to such integrated chemistry, a microchip (Lab-on-a-chip) having a fine groove used in various tests is called μ-TAS (Total Analytical System) if the use of the microchip is limited to analytical chemistry, and the microchip is called microreactor if the use of the microchip is limited to a reaction. When various tests, such as analyses, are carried out, integrated chemistry has advantages that the time to transport diffuse molecules is short due to small space and that the heat capacity of a liquid phase is very small. Therefore, integrated chemistry is noticed in the technical field wherein a micro space is intended to be utilized for carrying out analysis and chemical synthesis. Furthermore, the term “test” means to carry out any one or combination of operations and means, such as analysis, measurement, synthesis, decomposition, mixing, molecular transportation, solvent extraction, solid phase extraction, phase separation, phase combination, molecule acquisition, culture, heating and cooling.
In such integrated chemistry, a capillary electrophoresis chip used in a test in the field of, e.g., biochemistry, is a chip of a glass or plastic which has a fine groove or circular recessed portion having a width and depth of about 10 to 200 micrometers to use the fine groove or recessed portion as a liquid passage or reaction vessel to separate and identify a very small amount of vital material, such as a nucleic acid or protein, or another low molecular material, so that the material to be treated therein has a very small volume of nanoliters to picoliters. Therefore, it is required to precisely form the fine groove.
As methods for forming a fine groove (a hollow portion) in a glass or plastic, there are blow molding and lost-core methods. By these methods, it is difficult to precisely form a fine groove having a cross section tens micrometers square. Therefore, there is often adopted a method for forming a fine groove in a surface of a first plate member (a first member) of a glass, plastic or silicon to bond a second plate member (a second member), which is formed of the same material as that of the first plate member so as to have the same size as that of the first plate member, to the surface of the first plate member having the fine groove by adhesion or welding to form a microchip as a sample handling unit (see Japanese Patent Laid-Open Nos. 2000-246092 and 2000-288381).
However, if the sample handing device, which is formed by bonding the first plate member to the second plate member by adhesion or welding, slides down and drops from an experimenter's hand onto the floor or the like when various tests are carried out, the shock of the collision with the floor or the like causes external force, such as shearing force, to act on the bonded surface of the first plate member to the second plate member, so that there is the possibility that the bonded surface may be partially broken (cracked) to damage sealing performance around a microchannel to damage the function of the microchannel and/or to peel the first plate member off from the second plate member.
In recent years, there have been prosperously studied devices capable of carrying out separation, analysis, mixing, reaction, concentration or the like of a sample in a fine space called Lab-on-a-chip, μ-TAS, microreactor or the like. In such devices, there are many advantages in that the amount of a sample to be analyzed can be decreased, the size of system can be decreased, the time to carry out analysis or the like can be shortened, and so forth.
For example, there are known microfluidic devices for electrophoresis wherein a fine passage (microchannel) is formed in a fine space for separating and analyzing vital molecules, such as DNA and proteins, which serve as samples (specimens), and microfluidic devices for POC (Point-of-Care) wherein a reservoir or fine passage is formed for mixing a collected blood with a plurality of predetermined solutions to observe a catalytic reaction. Usually, these microfluidic devices have a single microfluidic system.
On the other hand, there are known microfluidic devices having a plurality of microfluidic systems (see WO99/15876, WO99/15888, and US 2003/0006141A1).
However, in these conventional devices, a large number of microchannels comprising fine grooves must be formed in a chip so as to be set in array. If such a chip having a large number of microchannels is intended to be formed by injection molding, it is difficult to work a die. Therefore, the cost of producing the die is very high, and the price of the chip is very high. Even if such a chip is formed by a working method other than injection molding, e.g., a working method utilizing a semiconductor working technique, such as photolithography, when a large number of microchannels comprising fine grooves are simultaneously formed in a chip (plate), the yields deteriorate to inhibit the price of the chip from decreasing.
In addition, in the above described conventional devices, a large number of microchannels are formed directly in a chip. Therefore, it is not possible to change the structure of the chip in accordance with intended purpose or the like, so that there is a problem in that the expensive chip can be only used for a specific intended purpose.